A Palestinian man removes a bag of flour from a house that was destroyed by an Israeli airstrike Thursday in Gaza City. The house’s owners were warned by the Israeli army to leave minutes before the missile hit.

GAZA CITY, Gaza Strip — Israel stepped up its campaign against Gaza’s ruling Hamas on Thursday, killing three of the group’s senior military commanders in an airstrike that pulverized a four-story home, the second such attack targeting top leaders in two days.

The pinpoint predawn attack on Hamas’ inner sanctum was launched minutes after the men emerged from tunnel hideouts, a security official said — displaying the long reach of Israel’s intelligence services.

The killing of the commanders, who played a key role in expanding Hamas’ military capabilities in recent years, was bound to lower morale in the secretive group but might not necessarily diminish its ability to fire rockets at Israel.

The strike Thursday in the southern Gaza town of Rafah, coupled with a Cabinet decision to call up 10,000 more reserve soldiers, signaled an escalation in the Israel-Hamas war after Egyptian cease-fire efforts collapsed this week.

Since July 8, more than 2,000 Palestinian, most of them civilians, have died in the fighting, according to Palestinian officials and the U.N. Sixty-four Israeli soldiers, two Israeli civilians and a guest worker also have been killed.

Meanwhile, a senior Hamas leader in exile admitted that Hamas was behind the kidnapping and killing of three Israeli teens in the West Bank — the group’s first claim of responsibility for the June attack that triggered an Israeli crackdown and eventually led to the Gaza war.

Saleh Arouri told an international conference of Islamic scholars in Turkey on Wednesday that Hamas grabbed the teens in hopes of sparking a Palestinian uprising in the West Bank.

The resumption of Gaza fighting came after several failed rounds of indirect talks of Israel and Hamas in Cairo.

Egyptian mediators had proposed that in exchange for quiet on the Israel-Gaza border, Israel gradually ease a border blockade it had imposed on Gaza, alongside Egypt, after Hamas seized the territory in 2007. Hamas rejected the proposal, saying Israel didn’t offer anything specific.

On Thursday, more than 100 rockets were fired from Gaza, while Israel carried out about 50 airstrikes, the Israeli military said. In all, at least 26 Palestinians were killed Thursday, among them six children.

In Gaza, one of those pulled from the rubble Thursday was Sara Deif, the 5-year-old daughter of Mohammed Deif, the top Hamas military leader who was apparently the target of an airstrike on a three-story home in Gaza City late Tuesday. Deif’s wife and infant son were also killed in the attack.

After the airstrike Thursday in Rafah, the Hamas military wing, the Izzedine al-Qassam Brigades, announced that three senior commanders — Mohammed Abu Shamaleh, Raed Attar and Mohammed Barhoum — had been killed.